This invention relates to high-modulus fiber metal matrix composites for use as backing plates with physical vapor deposition targets and for use in constructions with semiconductor substrates. The invention also pertains to utilization of high-modulus fiber metal matrix composites in packaging applications, with the composites being used as, for example lids, heat spreaders and heat sinks.
A normal PVD target assembly comprises a target and a backing plate. The target can be joined to the backing plate using mechanical, epoxy, solder or solid state diffusion. General requirements for the joint are high electrical and thermal conductivity, little or no distortion during sputtering, and good mechanical support. Mechanical joining provides a convenient mechanical support, but does not have good thermal and electrical conductivity, and so finds only limited application. Epoxy joining is easy, but an epoxy joint does not usually have good thermal and electrical properties. Solder and diffusion are the two most widely used methods for joining a target to a backing plate.
General requirements for the backing plate are high thermal and electrical conductivity, good mechanical strength, and most importantly, a coefficient of thermal expansion that closely matches the coefficient of thermal expansion of the target material. Target materials can comprise metal, consist essentially of metal, or consist of metal; and can comprise, for example, one or more of aluminum, copper, titanium, tungsten, tantalum, gold, and alloys thereof. Target materials can also, or alternatively, consist of, consist essentially of, or comprise, ceramic materials, such as, for example, lead, zirconate, and titanate (PZT); lead, lanthanum, zirconate, and titanate (PLZT); strontium barium tantalate (SBT); and barium strontium titanate (BST).
Materials such as aluminum, copper and molybdenum have been used as backing plate materials, but all have drawbacks due to either poor match to the physical properties of the target material or excessive cost. It would therefore be desirable to develop alternative backing plate materials.
The invention includes metal matrix composite backing materials for physical vapor deposition targets and for use in constructions with semiconductor substrates. The metal matrix composite backing materials of the present invention, can be used as, for example, microelectronics packaging lids, heat spreaders, and heat sinks. The metal matrix composite materials are constructed using a mixture of metal powder (Cu, Al, Ni, Ag, Ti, Co or an alloy of Cu, Al, Ni, Ag, Ti, Co) ranging in size from about xe2x88x92325 mesh size to about 100 mesh size, and discontinuous high-modulus material fibers, such as carbon, SiC, SiN, AlO, TiN, B, or combinations thereof, with fiber lengths ranging from about 10 microns to about 10 millimeters, and diameters ranging from about 1 micron to about 25 microns. It is noted that the listed fiber material compounds are described in terms of the materials in the compounds, rather in a specific stoichiometry. Thus, for example, the listed AlO can be Al2O3.
Depending on the application, the metal matrix composite materials can have a composition ranging from 1% by volume fiber to 70% by volume fiber. The materials can be consolidated by use of an axial loading method such as vacuum hot-press (preferred method), hot press, or squeeze casting. The terms xe2x80x9chot pressxe2x80x9d and xe2x80x9cvacuum hot pressxe2x80x9d refer to processes in which powdered metal is compressed to form a structure without melting of the metal, and the term xe2x80x9csqueeze castingxe2x80x9d refers to a process wherein a molten metal is solidified under pressure to form a structure. When the metal material is copper and the fibers are carbon, the consolidated materials can have a coefficient of thermal expansion that ranges from about 3xc3x9710xe2x88x926/xc2x0 C. to about 17xc3x9710xe2x88x926/xc2x0 C.; depending on carbon fiber volume and alignment. Thermal conductivity can range from about 130 W/mK (watts/meter-Kelvin) to over 400 W/mK, depending on, for example, carbon fiber volume and alignment. The density of the composite material can range from about 4.9 g/cc (gram/cubic centimeter) to about 7.6 g/cc.